It's pity that most developers shy away from these kinds of systems even when they initially pitch their games as such.
Mechajammer (aka Copper Dreams) and demo of Slaves of Magic had some promise for asynchcroniuous turns, but both shied away from that.
Some thoughts about WEGO, maybe I'm wrong.
In blobbers WEGO obviously works. In this case we're mostly talking about simultaneous choices and sequential resolution (EDIT : if the resolution was simultaneous then a character who died "before" performing his action during the current round would still perform his action, that can be done just as easily and would certainly work but that's generally not the case, probably because a game is more fun with sequential resolution) by the way.
However, is there even one WEGO classic D&D style RPG with positioning and melee combat out there which works? Or at least a wargame but which is quite close to that, not any wargame? I am really not an expert but my impression is that with positioning all the provided examples of WEGO seem to be something else, tactic games which work quite differently such as Battle Isle, Power, Breach & Clear or Frozen Synapse, with some specific combat mechanics with very specific targetting systems, they're not games with classic choices of a combat action leave alone classic targetting. I think that with Mechajammer and they're probably not the only ones when they start really thinking about everything it implies regarding targetting especially then they eventually realise the result would not be what they envisioned at all then they switch to something else more traditional. I think it's not as easy to do as people say, even if once again I may be wrong.
Some things can work in theory, like simultaneous vague choice of action (a character chooses to cast a fireball) but sequential resolution and targetting during resolution (only when it resolves the character chooses the area of effect) or simultaneous movement then simultaneous actions but the characters won't move during actions but these things seem worse than a traditional turn-based system to me, and you're doing that because you'd like to do WEGO but that's finally nothing like WEGO anyway so it is pointless.
There's one specific thing I'd like to talk about though'.
One thing I really like about WEGO with sequential resolution is that you can take into account the speed of the chosen actions to compute initiative order (even if unfortunately my impression from both playing blobbers and reading the manuals of these games is that they mostly don't).
In the vein of what I described above you can include such mechanics in a turn-based game, characters vaguely choose an action (move + melee, cast a fireball) then you roll for initiative taking the speed of the actions and then the resolution (targetting, especially) is executed sequencially. Let's take the precise situation where you want some randomness in how some characters will manage to escape from a fireball or not. Then this is not strictly the same than having, typically, preparation times, an area of effect decided when launching the spell (not when it resolves) and for whatever reason some randomness and/or hidden information put into those. I think that's vaguely interesting, and it is also interesting when playing P&P, but I am not certain it's really interesting in a video game and it's, in my opinion, again not WEGO anyway.